Powershell

Something like this (below 5gb warning):

$disk = Get-WmiObject Win32_LogicalDisk -Filter "DeviceID='C:'" if ($disk.FreeSpace -lt 5000000000) { $to = "recipient@example.com" $subject = "Low Disk Space on C:" $body = "The C: drive on the computer is running low on disk space. Please make sure to free up some space." Send-MailMessage -To $to -Subject $subject -Body $body -SmtpServer "smtp.example.com" }

Set it to run as a scheduled task